The Kamoer X1 pumps are fantastic. I've gone through a few dosing pumps in my day before settling on them. Price isn't too ridiculous, they're relatively easy to calibrate, easy to set up and very reliable. I'd recommend those for your three-element dosing. Personally I'd avoid the Jebao doser. Yes, it's cheap, and if you get lucky you can get a reliable unit that lasts you a while. Look around, though, and you'll see that a lot of people did not get lucky. Myself, for example. My Jebao wouldn't hold its calibration and frequently failed to even dose when it was supposed to. I spent more time cleaning the hoses out and re-priming and calibrating them than I did dosing.
My experience isn't universal, but the thing with Jebao is you never know what you're going to get... might get a good unit, might get crap. That's the gamble you take with them.
For an auto water change, I'm not sure that I'd try that without some kind of controller - either a dedicated AWC controller, or an Apex/GHL, etc. The problem is that with an AWC, you have to balance the output of two pumps to prevent imbalances over time. It's not an intractable problem - plenty of people have solved it - but there's a reason that most people who are doing AWC have an Apex or something like it. It's just much easier when you have integrated sensors that can detect when you've pulled out enough water and when you've replaced the correct amount of water.
Even if you get two identical pumps, they won't necessarily pump at the same rate, especially over time. So if you start off with two pumps that are supposed to pump 30 gph... after a month, maybe one degrades to 25 gph. Doesn't seem like much, but you'll eventually mess up your salinity over the course of several weeks. Yes, you can correct for it, but in my mind the whole point of an AWC is to avoid constant tinkering. If you're having to constantly adjust your timer, adjust the salinity in your replacement water, etc., you're kind of defeating the point of an AWC system.